The close association between neurons and glial cells suggests the existence of a symbiotic relationship between these cells in the nervous system. The main objective of the proposed research is to elucidate the role of neuron-Muller (glial) cell interactions in development and function of the vertebrate retina. Previous studies have shown that the glial intermediate filament protein (GFAP) gene is not normally expressed in Muller cells but is upregulated following photoreceptor degeneration. The cis-acting elements and transcription factors involved in GFAP induction are not known. Recent cell transfection studies with GFAP- luciferase plasmids and transgenic mice carrying GFAP regulatory sequences fused to lacZ gene show that cis elements in the 5' flanking sequence of the GFAP gene determine GFAP transcription in astrocytes but not in Muller cells. The main goal of the proposed research is to identify the genetic regulatory elements responsible for GFAP gene expression in Muller cells. Preliminary studies suggest that regulatory sequences present in approximately 10 Kb, 5' distal fragment can drive GFAP expression in Muller cell cultures. The present proposal is aimed at mapping and subsequent identification of the Muller cell-specific cis element contained in the 10 kb fragment. Truncated DNA sequences obtained by enzymatic manipulation of the 10 kb fragment will be fused to luciferase gene and tested by transfection into Muller cell cultures. To determine whether DNA sequences active in cell transfection function similarly in vivo, the DNA sequences will be tested in GFAP-lacZ transgenic mice. These studies should result in identification of the Muller cell-specific GFAP regulatory element. Since CFAP is a sensitive, widespread indicator of pathological changes in the retina, a clear knowledge of the factors that regulate GFAP expression is crucial for understanding pathophysiological changes observed in human retinal diseases.